This proposal describes a multifaceted approach to the study of root surface caries encompassing a variety of highly relevant clinical, laboratory, and animal studies which bring together expertise in clinical trials, microbiology, immunology, biochemistry, physical chemistry, histology, and electron miroscopy. The hub of the effort will be the clinical component: adult subjects will be screened and the data used to develop a general model relating root caries to putatively associated factors. Additionally, special risk groups will be studied to assess and characterize the disease in extremis. In the course of the clinical screenings subjects who appear particularly appropriate for further investigation will be recruited for a core group of paid volunteers who will be monitored longitudinally over the program. These individuals will serve as subjects for a series of microbiological, immunological and chemical studies. A primary purpose of the microbiological effort is to describe microbial populations of root surface plaque and to detect change in these populations associated with the development of lesions. Additional studies will deal with the phenomenon of bacterial attachment. Investigations utilizing the gnotobiotic model will focus on the interrelationships of Actinomyces and streptococci in the development of root caries. The effects of fluoride on root surface microflora will also be studied. The immunological phase will seek to characterize the local and systemic immune responses to the microorganisms associated with the disease. Physiochemical studies will attempt to determine the properties of demineralizing media required to induce in vivo-like lesions in extracted roots. All of the foregoing will be paralleled by studies aimed at establishing the histology and ultrastructure of tissue invasion and destruction in root caries.